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Dependence


Average autocorrelations across 20 series. (Taylor, 2005)

Autocorrelation of Returns

The autocorrelation (also known as serial correlation, serial dependence or mean aversion/mean reversion) of price changes (and therefore log returns) is insignificant. In light of the weak form of the efficient markets hypothesis, this is not surprising.

Autocorrelation of Absolute and Squared Returns

In contrast to the lack of dependence in returns, the autocorrelation for the absolute and squared returns is always positive and significant, and decays slowly. In addition, the autocorrelation in the absolute returns is generally higher than the autocorrelation in the corresponding squared returns.
Autocorrelations of absolute and squared returns; averages across 20 series. (Taylor, 2005)

[daily] "By contrast, for the absolute and squared returns, the autocorrelations start off at a moderate level (the first-order autocorrelation generally ranges between 0.2 and 0.3 for the stock returns and 0.1 and 0.2 for the exchange rate returns) but remain (significantly) positive for a substantial number of lags. In addition, the autocorrelation in the absolute returns is generally somewhat higher than the autocorrelation in the squared returns, especially for the stock market indices. This illustrates what has become known as the ‘Taylor property’ (see Taylor, 1986, pp. 52-5) - that is, when calculating the autocorrelations for the series |yt|δ| for various values of δ, one almost invariably finds that the autocorrelations are largest for δ = 1."
Frances and van Dijk (2000) page 30

[daily stock returns] "The autocorrelations in the absolute and squared return series are always much higher than those in the return series, and they are consistently significantly positive for lags up to 60 days. The autocorrelation between absolute returns, however, is generally higher than that in squared returns."
[daily stock returns] "...the autocorrelations in the series of equal-weighted index returns are generally higher than those in the value-weighted series."
Akgiray (1989)

"slow decay of the autocorrelation of absolute value of price-changes"
Johnson, Jefferies and Hui (2003), page 69

Liu, et al. (1997) analyzed absolute returns of the S&P500 at 1 minute intervals and found that the correlations can be described by two different power laws with a crossover time of 600 minutes.

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